An aesthetic view is one of important matters in current dental treatments. Dental materials are strongly desired to have adequate color tone comparable with natural teeth or exhibit a beautiful color of white.
To meet the needs of the aesthetic view, instead of dental metals ceramics or resin materials are used as a dental restorative material. In such a way, a natural dental crown color is reproduced. Particularly, resin materials have been extensively developed. In recent years, some of resin materials have a sufficient abrasion resistance, bending strength, and water resistance.
Particularly, the resin materials are very often used to form facing crowns. Facing crowns are a crown restoration that is a sort of dental veneers. The outer part of the facing crowns is formed from a teeth crown material such as resin materials. As a result, the facing crowns provide not only adequate functions in the oral cavity but also adequate aesthetic. A preparation procedure is illustrated below.
First, an appropriate pre-treatment such as sandblasting is applied to a metal cast called a metal frame and then, a primer for bonding metal is applied to the treatment surface with a brush.
Retention beads may be attached to the surface of the metal frame in order to obtain an irregular surface which yields an increased mechanical bond to a resin material. A preopaque material may be applied and cured on the surface to which retention beads are applied in order to fill several voids between retention beads and to enhance the adhesion strength. Subsequently, to conceal the metal color of the metal frame, an opaque material is applied and cured which consists of a hardening composition and has a high contrast ratio. The procedure of applying and curing such hardening composition in the paste form is repeated as required. After an adequate concealment of the metal color is obtained, a hardening resin paste for forming dental crown is gradually rebuilt-up and cured on the cured form of the resin. The process is, as required, repeated to finally make a teeth form (non-patent literature 1).
If the adhesive strength is not adequate between the metal frame and the opaque material, the cured form of the opaque material or hardening resin paste is peeled off from the surface of the metal. As a result, remaking of a teeth form is required. Alternatively, a dye caused from food and drink gets into an interspace between the metal frame and the cured form of the opaque material and the aesthetic view becomes inadequate.
Several primers for bonding metal having high properties have been developed (patent literatures 1, 2, and 3). However, there are still problems including chippage of cured resins, peel-off from metal frames, and inadequate appearance due to stains which may be caused from a poor adhesive strength between cured resins and metal frames. It is thought that these problems may be caused in part from inadequate adherence properties between primers for bonding metal and opaque materials.
In addition, a good operability in use is an important factor for opaque materials when in the paste form. If opaque materials have inadequate operability, it is difficult to uniformly apply the opaque material, possibly resulting in a poor adhesive strength and inadequate aesthetic view. If the opaque materials exhibit an adhesive property, surface hardness, mechanical strength, and aesthetic view become inadequate.
Several different opaque materials and opaque sets as opaque composition have been developed (patent literatures 4, 5, 6, and 7). However, opaque compositions comprising one type of opaque material have a tendency to decrease in adhesive strength as compared to opaque compositions comprising two or three types of opaque materials. In view of operability, such one-type opaque compositions do not fully fill voids between several retention beads which are attached to a surface of dental materials. Further, one-type compositions easily droop because of a low viscosity in the paste form, which is inadequate as an obscure material. Such inadequate property may be improved by combining two or three type of opaque materials. There are still problems regarding operability in the paste form, color tone reproduction, and mechanical strength.
Moreover, a hard resin is applied and polymelized to make an upper construction. In the procedure, a metal instrument generally used to make the upper construction. The metal instrument is shaved at edges of filler particles comprised in the hardened opaque materials and the surface of the hardened opaque materials is stained with black color, resulting in a poor aesthetic view.
An important problem to be solved is to provide an opaque material set that exhibits a good durable adhesiveness, adhesive strength and good color tone reproduction comparable with natural dental crowns as well as have a good operability. In late years, a hard resin has a good color tone reproduction in that the hardened materials exhibit white color similar or superior to natural dental crowns. It is important for opaque materials to have a good property so that metal colors of metal frames are concealed. Opaque materials are expected to adequately conceal metal colors and to reproduce color tone and transparency of upper constructions. Accordingly, there are needs for an opaque material set or composition to fill voids between several retention beads and exhibit a good mechanical strength, have an adequate concealment of color, reproduce a color tone comparable with natural dental crowns, and a reproducible operability so that an opaque material is thinly applied.